In the drilling of an oil well through a production zone which is thought to be suitable for production, it is often desirable to run a test of the production zone for the express purpose of determining production potential. This typically occurs at the stage after the well has been drilled but all of the production equipment has not been installed. The formation of interest is typically packed off by setting isolation packers above and below the zone of interest. A test string is installed above the zone and incorporates a receptacle for receiving a surface readout probe which is lowered on a wire line. The initial condition finds the production zone of interest shut in, that is, without flow from the zone to the surface. This investigative step is usually implemented after packing off the production zone so that there is no flow in the open hole, and pressure control apparatus is installed at the well head. Typically, this includes a lubricator and blow out preventer assembly. A wire line is fed through the production equipment at the surface and is lowered into the well to support a probe on the wire line. The wire line is run into the well to land the probe in a cooperative fashion at the test string equipment installed in the well.
Through the use of the present invention, the formation of interest is produced and flowed for a regulated interval. Certain pressures and temperatures are recorded. while the probe remains engaged with the test string equipment in the well, data is collected by the probe and is fed up the wire line. This data is delivered to the surface and a plot is formed of pressure against time. Such a plot has great value for the purpose of determining through a Horner straight line plot whether the test flow has had sufficient duration, leading to the determination of the well potential for oil or gas production.
One of the handicaps which is encountered is that fairly ruggedized equipment must be used and operated through a high pressure lubricator. This typically involves the use of an armored wire line as small as 7/32 inches to reduce the size of the cross sectional area presented under pressure to the high pressure lubricator. This is typically a single center conductor armored cable. The wire line is required to support the weight of the probe and to operate the probe with the test string equipment located downhole. Equally important, data is collected by transfer along the wire line. The center conductor of the wire line is therefore a common conductor which is used to transfer data and power. The wire line is used as a single conductor for data transfer in both directions and to provide electric power for operation of the probe. A complete circuit is obtained utilizing the armored sheath of the single conductor wire line. This single conductor therefore is connected to several components of equipment in the probe with a goal of of sorting out the signals which are transferred to and from the downhole equipment and the surface equipment.